Rollup merge of #52907 - pnkfelix:issue-52877-original-source-should-precede-suggestions, r=petrochenkov

NLL: On "cannot move out of type" error, print original before rewrite

NLL: On "cannot move out of type" error, print original source before rewrite.

 * Arguably this change is sometimes injecting noise into the output  (namely in the cases where the suggested rewrite is inline with the   suggestion and we end up highlighting the original source code).   I would not be opposed to something more aggressive/dynamic, like   revising the suggestion code to automatically print the original  source when necessary (e.g. when the error does not have a span   that includes the span of the suggestion).

 * Also, as another note on this change: The doc comment for `Diagnostic::span_suggestion`  says:
```rust
    /// The message
    ///
    /// * should not end in any punctuation (a `:` is added automatically)
    /// * should not be a question
    /// * should not contain any parts like "the following", "as shown"
```
  *  but the `:` is *not* added when the emitted line appears  out-of-line relative to the suggestion. I find that to be an  unfortunate UI experience.

----

As a drive-by fix, also changed code to combine multiple suggestions for a pattern into a single multipart suggestion (which vastly improves user experience IMO).

----

Includes the updates to expected NLL diagnostics.

Fix #52877

8 files changed, 86 insertions, 44 deletions

diff --git a/src/librustc_mir/borrow_check/move_errors.rs b/src/librustc_mir/borrow_check/move_errors.rs
index 103f431d4ba..4d988fef450 100644
--- a/src/librustc_mir/borrow_check/move_errors.rs
+++ b/src/librustc_mir/borrow_check/move_errors.rs
@@ -341,7 +341,8 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
                 // another match arm
                 binds_to.sort();
                 binds_to.dedup();
-                for local in binds_to {
+                let mut multipart_suggestion = Vec::with_capacity(binds_to.len());
+                for (j, local) in binds_to.into_iter().enumerate() {
                     let bind_to = &self.mir.local_decls[local];
                     let binding_span = bind_to.source_info.span;
 
@@ -350,13 +351,15 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
                         Mutability::Not => "ref",
                         Mutability::Mut => "ref mut",
                     };
+                    if j == 0 {
+                        err.span_label(binding_span, format!("data moved here"));
+                    } else {
+                        err.span_label(binding_span, format!("... and here"));
+                    }
                     match bind_to.name {
                         Some(name) => {
-                            err.span_suggestion(
-                                binding_span,
-                                "to prevent move, use ref or ref mut",
-                                format!("{} {:?}", ref_kind, name),
-                            );
+                            multipart_suggestion.push((binding_span,
+                                                       format!("{} {}", ref_kind, name)));
                         }
                         None => {
                             err.span_label(
@@ -366,6 +369,8 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
                         }
                     }
                 }
+                err.multipart_suggestion("to prevent move, use ref or ref mut",
+                                         multipart_suggestion);
             }
             // Nothing to suggest.
             GroupedMoveError::OtherIllegalMove { .. } => (),
diff --git a/src/test/ui/borrowck/borrowck-move-error-with-note.nll.stderr b/src/test/ui/borrowck/borrowck-move-error-with-note.nll.stderr
index a34c97974da..1b913471924 100644
--- a/src/test/ui/borrowck/borrowck-move-error-with-note.nll.stderr
+++ b/src/test/ui/borrowck/borrowck-move-error-with-note.nll.stderr
@@ -19,14 +19,16 @@ error[E0509]: cannot move out of type `S`, which implements the `Drop` trait
    |
 LL |     match (S {f: "foo".to_string(), g: "bar".to_string()}) {
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot move out of here
+...
+LL |             f: _s,
+   |                -- data moved here
+LL |             g: _t
+   |                -- ... and here
 help: to prevent move, use ref or ref mut
    |
 LL |             f: ref _s,
-   |                ^^^^^^
-help: to prevent move, use ref or ref mut
-   |
 LL |             g: ref _t
-   |                ^^^^^^
+   |
 
 error[E0507]: cannot move out of borrowed content
   --> $DIR/borrowck-move-error-with-note.rs:57:11
diff --git a/src/test/ui/borrowck/borrowck-move-out-of-vec-tail.nll.stderr b/src/test/ui/borrowck/borrowck-move-out-of-vec-tail.nll.stderr
index d01b24507d9..95a7894d532 100644
--- a/src/test/ui/borrowck/borrowck-move-out-of-vec-tail.nll.stderr
+++ b/src/test/ui/borrowck/borrowck-move-out-of-vec-tail.nll.stderr
@@ -3,14 +3,19 @@ error[E0508]: cannot move out of type `[Foo]`, a non-copy slice
    |
 LL |             match tail {
    |                   ^^^^ cannot move out of here
+LL |                 &[Foo { string: a },
+   |                                 - data moved here
+...
+LL |                   Foo { string: b }] => {
+   |                                 - ... and here
 help: to prevent move, use ref or ref mut
    |
 LL |                 &[Foo { string: ref a },
-   |                                 ^^^^^
-help: to prevent move, use ref or ref mut
-   |
+LL |                 //~^ ERROR cannot move out of type `[Foo]`
+LL |                 //~| cannot move out
+LL |                 //~| to prevent move
 LL |                   Foo { string: ref b }] => {
-   |                                 ^^^^^
+   |
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/borrowck/borrowck-vec-pattern-nesting.nll.stderr b/src/test/ui/borrowck/borrowck-vec-pattern-nesting.nll.stderr
index 50ef3ba40e7..2779132590e 100644
--- a/src/test/ui/borrowck/borrowck-vec-pattern-nesting.nll.stderr
+++ b/src/test/ui/borrowck/borrowck-vec-pattern-nesting.nll.stderr
@@ -28,7 +28,10 @@ error[E0508]: cannot move out of type `[std::boxed::Box<isize>]`, a non-copy sli
 LL |     match vec {
    |           ^^^ cannot move out of here
 LL |         &mut [_a, //~ ERROR cannot move out
-   |               -- help: to prevent move, use ref or ref mut: `ref _a`
+   |               --
+   |               |
+   |               data moved here
+   |               help: to prevent move, use ref or ref mut: `ref _a`
 
 error[E0508]: cannot move out of type `[std::boxed::Box<isize>]`, a non-copy slice
   --> $DIR/borrowck-vec-pattern-nesting.rs:57:13
@@ -46,7 +49,10 @@ LL |     match vec {
    |           ^^^ cannot move out of here
 ...
 LL |          _b] => {}
-   |          -- help: to prevent move, use ref or ref mut: `ref _b`
+   |          --
+   |          |
+   |          data moved here
+   |          help: to prevent move, use ref or ref mut: `ref _b`
 
 error[E0508]: cannot move out of type `[std::boxed::Box<isize>]`, a non-copy slice
   --> $DIR/borrowck-vec-pattern-nesting.rs:70:13
@@ -62,18 +68,15 @@ error[E0508]: cannot move out of type `[std::boxed::Box<isize>]`, a non-copy sli
    |
 LL |     match vec {
    |           ^^^ cannot move out of here
+LL |         &mut [_a, _b, _c] => {}  //~ ERROR cannot move out
+   |               --  --  -- ... and here
+   |               |   |
+   |               |   ... and here
+   |               data moved here
 help: to prevent move, use ref or ref mut
    |
-LL |         &mut [ref _a, _b, _c] => {}  //~ ERROR cannot move out
-   |               ^^^^^^
-help: to prevent move, use ref or ref mut
-   |
-LL |         &mut [_a, ref _b, _c] => {}  //~ ERROR cannot move out
-   |                   ^^^^^^
-help: to prevent move, use ref or ref mut
-   |
-LL |         &mut [_a, _b, ref _c] => {}  //~ ERROR cannot move out
-   |                       ^^^^^^
+LL |         &mut [ref _a, ref _b, ref _c] => {}  //~ ERROR cannot move out
+   |               ^^^^^^  ^^^^^^  ^^^^^^
 
 error[E0508]: cannot move out of type `[std::boxed::Box<isize>]`, a non-copy slice
   --> $DIR/borrowck-vec-pattern-nesting.rs:82:13
diff --git a/src/test/ui/borrowck/issue-51415.nll.stderr b/src/test/ui/borrowck/issue-51415.nll.stderr
index d872c7efe2b..20713c3392e 100644
--- a/src/test/ui/borrowck/issue-51415.nll.stderr
+++ b/src/test/ui/borrowck/issue-51415.nll.stderr
@@ -4,6 +4,7 @@ error[E0507]: cannot move out of borrowed content
 LL |     let opt = a.iter().enumerate().find(|(_, &s)| {
    |                                          ^^^^^-^
    |                                          |    |
+   |                                          |    data moved here
    |                                          |    help: to prevent move, use ref or ref mut: `ref s`
    |                                          cannot move out of borrowed content
 
diff --git a/src/test/ui/codemap_tests/overlapping_spans.nll.stderr b/src/test/ui/codemap_tests/overlapping_spans.nll.stderr
index 34616a8de45..a1fbcf1430d 100644
--- a/src/test/ui/codemap_tests/overlapping_spans.nll.stderr
+++ b/src/test/ui/codemap_tests/overlapping_spans.nll.stderr
@@ -4,7 +4,10 @@ error[E0509]: cannot move out of type `S`, which implements the `Drop` trait
 LL |     match (S {f:"foo".to_string()}) {
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^ cannot move out of here
 LL |         S {f:_s} => {} //~ ERROR cannot move out
-   |              -- help: to prevent move, use ref or ref mut: `ref _s`
+   |              --
+   |              |
+   |              data moved here
+   |              help: to prevent move, use ref or ref mut: `ref _s`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issue-12567.nll.stderr b/src/test/ui/issue-12567.nll.stderr
index a040f7c3c8d..29bda252b91 100644
--- a/src/test/ui/issue-12567.nll.stderr
+++ b/src/test/ui/issue-12567.nll.stderr
@@ -3,28 +3,40 @@ error[E0508]: cannot move out of type `[T]`, a non-copy slice
    |
 LL |     match (l1, l2) {
    |           ^^^^^^^^ cannot move out of here
+LL |         (&[], &[]) => println!("both empty"),
+LL |         (&[], &[hd, ..]) | (&[hd, ..], &[])
+   |                 -- data moved here
+...
+LL |         (&[hd1, ..], &[hd2, ..])
+   |                        --- ... and here
 help: to prevent move, use ref or ref mut
    |
 LL |         (&[], &[ref hd, ..]) | (&[hd, ..], &[])
-   |                 ^^^^^^
-help: to prevent move, use ref or ref mut
-   |
+LL |             => println!("one empty"),
+LL |         //~^^ ERROR: cannot move out of type `[T]`, a non-copy slice
+LL |         //~^^^ ERROR: cannot move out of type `[T]`, a non-copy slice
 LL |         (&[hd1, ..], &[ref hd2, ..])
-   |                        ^^^^^^^
+   |
 
 error[E0508]: cannot move out of type `[T]`, a non-copy slice
   --> $DIR/issue-12567.rs:14:11
    |
 LL |     match (l1, l2) {
    |           ^^^^^^^^ cannot move out of here
+LL |         (&[], &[]) => println!("both empty"),
+LL |         (&[], &[hd, ..]) | (&[hd, ..], &[])
+   |                 -- data moved here
+...
+LL |         (&[hd1, ..], &[hd2, ..])
+   |            --- ... and here
 help: to prevent move, use ref or ref mut
    |
 LL |         (&[], &[ref hd, ..]) | (&[hd, ..], &[])
-   |                 ^^^^^^
-help: to prevent move, use ref or ref mut
-   |
+LL |             => println!("one empty"),
+LL |         //~^^ ERROR: cannot move out of type `[T]`, a non-copy slice
+LL |         //~^^^ ERROR: cannot move out of type `[T]`, a non-copy slice
 LL |         (&[ref hd1, ..], &[hd2, ..])
-   |            ^^^^^^^
+   |
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/nll/move-errors.stderr b/src/test/ui/nll/move-errors.stderr
index 3f2c651ae3a..53d60d3f6d6 100644
--- a/src/test/ui/nll/move-errors.stderr
+++ b/src/test/ui/nll/move-errors.stderr
@@ -59,6 +59,7 @@ error[E0509]: cannot move out of type `D`, which implements the `Drop` trait
 LL |     let C(D(s)) = c;
    |             -     ^ cannot move out of here
    |             |
+   |             data moved here
    |             help: to prevent move, use ref or ref mut: `ref s`
 
 error[E0507]: cannot move out of borrowed content
@@ -88,7 +89,10 @@ LL |     match x {
    |           ^ cannot move out of here
 ...
 LL |         B::U(D(s)) => (),
-   |                - help: to prevent move, use ref or ref mut: `ref s`
+   |                -
+   |                |
+   |                data moved here
+   |                help: to prevent move, use ref or ref mut: `ref s`
 
 error[E0509]: cannot move out of type `D`, which implements the `Drop` trait
   --> $DIR/move-errors.rs:105:11
@@ -97,7 +101,10 @@ LL |     match x {
    |           ^ cannot move out of here
 ...
 LL |         (D(s), &t) => (),
-   |            - help: to prevent move, use ref or ref mut: `ref s`
+   |            -
+   |            |
+   |            data moved here
+   |            help: to prevent move, use ref or ref mut: `ref s`
 
 error[E0507]: cannot move out of borrowed content
   --> $DIR/move-errors.rs:105:11
@@ -106,21 +113,25 @@ LL |     match x {
    |           ^ cannot move out of borrowed content
 ...
 LL |         (D(s), &t) => (),
-   |                 - help: to prevent move, use ref or ref mut: `ref t`
+   |                 -
+   |                 |
+   |                 data moved here
+   |                 help: to prevent move, use ref or ref mut: `ref t`
 
 error[E0509]: cannot move out of type `F`, which implements the `Drop` trait
   --> $DIR/move-errors.rs:115:11
    |
 LL |     match x {
    |           ^ cannot move out of here
+LL |     //~^ ERROR
+LL |         F(s, mut t) => (),
+   |           -  ----- ... and here
+   |           |
+   |           data moved here
 help: to prevent move, use ref or ref mut
    |
-LL |         F(ref s, mut t) => (),
-   |           ^^^^^
-help: to prevent move, use ref or ref mut
-   |
-LL |         F(s, ref mut t) => (),
-   |              ^^^^^^^^^
+LL |         F(ref s, ref mut t) => (),
+   |           ^^^^^  ^^^^^^^^^
 
 error[E0507]: cannot move out of borrowed content
   --> $DIR/move-errors.rs:123:11